OK, at the time I was somewhat staggered by the dumbness of this question. I gave a talk about my work, in which I described how various ion channels could be inhibited and potentiated by a selection of anesthetics. Then someone asked, essentially: If a drug has the capability to depolarize a neuron, potentially leading to increased firing, it can't act as an anesthetic, can it?
Now, this dude, given that he must be in anesthesiology research if he was at my talk, should have known better. And definitely should have known better than to ask it as if he had stumbled across a trick question that would unravel all my research, because that's just jerk-y.
But it actually isn't a dumb question. Unconsciousness is much more complicated than simple suppression of all neuronal activity. During anesthesia, some neurons fire more and some neurons fire less. And the hard truth is - we're not totally sure which neurons do what or how that leads to anesthetic endpoints. In general what changes is firing PATTERN, which causes changes in how neurons talk to each other ("integration" for those wanting a more technically accurate term).
Consciousness and anesthesia are so much more complicated than simple reduction in total brain activity, but that's what makes it fun!